The use of disposable test elements has become commonplace to measure the presence and/or concentrations of selected analytes in test samples. For example, patients suffering from diabetes and similar medical conditions often engage in self-monitoring of blood glucose where the patient monitors his or her blood glucose levels. The purpose of monitoring blood-glucose levels is to determine the concentration level, and if necessary to take corrective action if the level is too high or too low in order to bring the level back within an acceptable range. In addition, blood glucose levels are determined to calculate a pre-meal insulin bolus often with the help of a bolus calculator with the goal of minimizing glucose increases from consumption of the meal. The failure to take corrective action can have serious medical implications. Glucose monitoring is a fact of everyday life for diabetic individuals, and the accuracy of such monitoring can literally mean the difference between life and death. Failure to maintain blood glucose at acceptable levels on a regular basis can result in serious diabetes-related complications, including cardiovascular disease, kidney disease, nerve damage and blindness.
People with diabetes who intensively manage their blood sugar experience long-lasting benefits. The Diabetes Control and Complications Trial (DCCT) was a clinical study conducted from 1983 to 1993 by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). The DCCT compared intensive to conventional treatments. Patients on intensive treatment kept glucose levels as close to normal as possible with at least three insulin injections a day or an insulin pump, and frequent self-monitoring of blood glucose levels. Intensive treatment aimed to keep hemoglobin A1c (HbA1c), which reflects average blood glucose over a 2- to 3-month period, as close to normal as possible. Conventional treatment consisted of one or two insulin injections a day with once-a-day urine or blood glucose testing. The results of the DCCT study showed that keeping blood glucose levels as close to normal as possible slows the onset and progression of eye, kidney, and nerve diseases caused by diabetes. In fact, it demonstrated that any sustained lowering of blood glucose helps, even if the person has a history of poor control.
A number of analytical instruments or biosensors, such as glucose meters, are currently available that permit an individual to test the glucose level in a small sample of blood. Many of the meter designs currently available make use of a disposable test element which, in combination with the meter, measures the amount of glucose in the blood sample electrochemically or optically. In current glucose meters, the information displayed as a consequence of a successful blood glucose measurement is the respective blood glucose value, typically shown in mg/dL or mmol units, and perhaps the time and date the measurement was performed. This information, in combination with calculation of planned or known intake of carbohydrates or planned or known activities and knowledge of other situational or individual factors, is in most cases sufficient to allow diabetics to adjust or derive their dietary intake and/or an immediate dose of insulin to inject to control blood glucose level on the short-term. Also, in case of low glucose values, diabetics can detect the need for intake of sugar to avoid hypoglycemia.
An absence or insufficient amount of insulin prevents the body from using glucose as a fuel source to produce energy. When this occurs, the body produces energy by breaking down fatty acids, which results in ketone byproducts and increased ketone levels. Increased ketone levels in diabetics may also be caused by a heart attack, stroke, recreational drug usage or an intercurrent illness such as pneumonia, influenza, gastroenteritis, or a urological infection. Excessive ketone levels in diabetics leads to an episode of diabetic ketoacidosis (DKA), a medical emergency that can result in death if not treated. Symptoms of DKA include nausea, vomiting, excessive thirst and urine production, abdominal pain, labored breathing, fatigue, and coma, amongst others. Given the seriousness of DKA, it is desirable to administer treatment to reduce ketone levels before the full onset of a DKA episode. Further, since symptoms related to a DKA episode may not present until the DKA episode has onset or ketone levels are otherwise undesirably high, it is generally preferred for ketone reducing treatment not to begin as a response to these symptoms.
Prevention of DKA episodes can be achieved by measuring ketone levels and seeking medical attention if they rise above a certain concentration. The ADA website recommends that ketone levels should be checked every 4-6 hours when a diabetic has an illness (such as a cold or the flu), or when his or her blood glucose is more than 240 mg/dl. (See http://www.diabetes.org/living-with-diabetes/complications/ketoacidosis-dka.html). Urine tests can be utilized to determine ketone levels. However, for diabetics who perform multiple blood glucose tests per day, performing separate urine tests in addition to their blood glucose tests is time consuming and burdensome.
By having a dual test to measure glucose and ketone levels on the same test strip, a diabetic is better enabled to comply with testing recommendations and safer therapy by detecting high ketone levels early. For example, it is recommended to avoid exercise when ketone and blood glucose are high because elevated levels of these analytes may be indicative of unsatisfactory diabetes management. However, most diabetics do not have ketone tests readily available for testing, and often do not have information readily available for how to handle such situations. Furthermore, the symptoms of diabetic ketoacidosis usually evolve over about a 24 hour period, meaning useful information and instruction typically require the perspective of trending analysis.
The use of separate urine tests for determining ketone levels also requires additional diagnostic supplies and their attendant costs, and makes it difficult to correlate blood glucose and ketone levels. It is also possible to determine ketone levels from blood samples. When blood samples are used, ketone levels are commonly determined by measuring the concentration of hydroxybutyrate, which is the predominate ketone in blood. Hydroxybutyrate concentrations below 0.6 mM in blood are considered normal, while hydroxybutyrate concentrations that are between 0.6 mM and 1.5 mM indicate that a problem may develop and greater than 1.5 mM indicate a risk for developing DKA. Hydroxybutyrate concentrations above 3 mM in blood are indicative of DKA and require emergency medical treatment.
Current techniques for determining ketone levels from blood involve single function test elements that are suitable for detecting hydroxybutyrate concentrations for example. Much like the urine test described above however, diabetics who perform a relatively high magnitude of blood glucose tests per day may find it time consuming and burdensome to perform separate ketone level blood tests in addition to their blood glucose tests, particularly since current blood ketone tests are slower than state of the art blood glucose tests. Ketone level blood tests that are performed independent of blood glucose tests also require additional diagnostic supplies and additional expenses attendant therewith must be incurred. Moreover, performing separate tests for determining blood glucose and blood ketone levels makes it difficult to correlate the measured blood glucose and blood ketone values since, amongst other factors, they may not be measured within the same timeframe or may be performed using different devices.
Other techniques for determining ketone levels from blood involve test elements suitable for detecting blood glucose and blood ketone levels. In these current test elements however, blood glucose levels are measured more quickly than blood ketone levels such that the blood ketone test results are delayed and provided after the blood glucose test results. Alternatively, the results of both the blood glucose and blood ketone tests are not provided until the latter completion of the blood ketone test. In either case, waiting for the results of one or both tests until the blood ketone test is completed can become quite burdensome and time consuming for a diabetic who performs a relatively high magnitude of tests each day, particularly when considering that in some instances the blood ketone test can take almost twice as long to complete as the blood glucose test. Moreover, when the blood glucose test results are provided before and separate from the blood ketone test results, a possibility arises for a user to discontinue testing before the blood ketone test is completed and/or divert attention elsewhere after the blood glucose test results have been provided but before the results of the blood ketone test have been properly considered. In further instances, a user may be burdened by the automatic display of the blood ketone results following each test, which may lead to insufficient consideration or user depreciation of the importance of the blood ketone test results. As a corollary, burdening a diabetic patient with a ketone value for each measurement even when the majority of time it is in a normal range could cause a user to ignore the value at a time when it really requires attention.
Given the ramifications of accurate recording, reporting and analyzing of blood ketone measurements in addition to blood glucose measurements, improvements in the techniques, procedures and equipment for testing blood ketone levels and/or blood ketone and blood glucose levels are desired.